Environ. Sci. Technol. 1994, 28, 1968-1974
Boron Isotope Application for Tracing Sources of Contamination in Groundwater A. Vengosh,'rt K. G. Heumann,* S. Juraske,* and R. Kashers Research Department, Hydrological Service, P.O. Box 638 1, Jerusalem 9 1063, Israel, Institute of Inorganic Chemistry, University of Regensburg, Universitatsstrasse 3 1, 93040 Regensburg, Germany, and Department of Organic Chemistry, Hebrew University, Jerusalem 91904, Israel
Boron isotope composition and concentration of sewage effluent and pristine and contaminated groundwater from the Coastal Plain aquifer of Israel have been determined. The application of boron compounds, especially sodium perborate as a bleaching agent in detergents, leads to an enrichment of boron in wastewaters. Anthropogenic boron in wastewater is isotopically distinct from natural boron in groundwater and thus can be utilized to identify the source of contamination. It is shown that P B (where 611B = [(("B/loB),,,i~/(l'B/loB)~~~ 951) - 11 X 1000)values of raw and treated sewage effluents from the Dan Region Sewage Reclamation Project ( P B = 5.3-12.9%0)overlap those of natural nonmarine sodium borate minerals (-0.9% to +10.2%0)but differ significantly from those of regional uncontaminated groundwater (-3O%o) and seawater (39%). Groundwater contaminated by recharge of treated sewage yields a high B/C1 ratio with a distinctive anthropogenic isotopic signature ('7-25960;. Elemental B and 611B variations reflect both mixing with regional groundwater and boron isotopic fractionation associated with boron removal by adsorption onto clay minerals. The distinctive isotopic signature of anthropogenic boron can be recognized, however, in most samples and differs significantly from those of natural sources of contamination in the Coastal Plain aquifer of Israel, such as marine-derived saline groundwater (35-60%). This enables utilization of the boron isotope composition of groundwater as a tracer for identification and quantification of contaminants in groundwater.
Introduction One of the main goals of environmental protection is to prevent deterioration of water quality through early recognition of contamination sources. The variety of pollution sources, however, makes this task difficult. For example, the increase in the salinity of groundwater, particularly in coastal areas, can be a result of "natural" causes such as seawater intrusion, dissolution of soluble salts, upconing of saline water from adjacent aquifers, or anthropogenic contamination such as seepage of sewage effluent. This study is the first to utilize the isotopic composition of boron for tracing sewage effluent and contaminated groundwater from the Coastal Plain aquifer of Israel. Each of the contamination sources may be characterized by a readily distinguishable boron isotopic ratio (l1B/l0B); hence the use of boron isotopes might provide a sensitive method for evaluation and identification of contaminated groundwater. Natural boron has two stable isotopes, llB (abundance of 80.1%) and loB (19.9%). The relatively large mass + Hydrological Service. t University of Regensburg. 8 Hebrew University. lS68
Environ. Sci. Technol., Voi. 28, No. 11, 1994
Table 1. Chemical Compositions of Natural Borate Minerals and Synthetic Boron Products mineral
chemical composition
borax (tincal) ulexite colemanite inyoite sodium perborate tetrahydrate sodium perborate monohydrate
NazB40~10Hz0 NaCaB~Og43Hz0 CazB304(OH)r2HzO CaB303(0H)u4H20 NaBOr4HzO NaB0rH20
BzOz wt%
~~~~
36.5 43.0 50.8 37.6 22.5 34.0
__
difference between these isotopes results in a wide range of 6l'B values in natural waters, from -16% to +59%0(e.g., refs 1-10), Isotopic fractionation of boron is controlled by the exchange reactions of the boron species. IlB separates preferentially into dissolved boron in a solution [mainly composed of undissociated boric acid B(OH)3], whereas loB is preferentially incorporated in the form of the tetrahedral species in the solid phase (11-14). In previous studies different isotopic signatures have been used for tracing the sources of dissolved boron, and in particular to distinguish marine from nonmarine contributions (e.g., refs 1-8). Boron in groundwater might derive from leaching of country rocks, infiltration of meteoric cyclic salts, mixing with adjacent groundwater bodies, and contamination by anthropogenic sources (8, IO). Each natural source has a distinctive boron isotopic composition, e.g., seawater ( P B = 39%) uersus average continental crust ( P B x 0 f 5%). The boron isotope composition of anthropogenic sources has not yet been well delineated. The only data are those reported for fly ashleachates from the United States having a P B range of -7.9%0 to 15.8% (four analyses; ref 8). Boric acid and borate minerals are widely utilized in a number of industrial applications such as glass and porcelain manufacture, production of leather, carpets, cosmetics, and photographic chemicals, fertilizers, wire drawing, and welding and brazing of metals. The main application of boron is, however, the use of sodium perborate (Table 1) as an oxidation bleaching agent in domestic and industrial cleaning products (15). The discharge of sodium perborate into the environment during production and end use of detergents has resulted in the accumulation of boron in waste effluents and consequently in natural aquatic systems. More than 790 000 tons of sodium perborate were used in western Europe alone during 1985 (16),i.e., an annual discharge of anthropogenic boron of 1011 g of B/yr, assuming that all of the boron contained in detergents enters the environment directly via the sewage systems. By way of comparison, the estimated natural boron influx into the oceans, based on the sum of oceanic boron sinks (ocean crust alteration, adsorption on detrital sediments, precipitation of calcium carbonate), is on the order of 3 X 10l1g of B/yr (17).Thus, a substantial amount of anthropogenic boron, comparable
-
0013-936X/94/0928-1966$04.50/0
0 1994 American Chemical Soclety
EIias '61 Levitin
-4
0
5OOm
b
Observation well Pipeline
- Expressway
Gon Soreq
.
Dan 2 Well name 237 Chloride content
Figure 1. Locationmaps of wells and spreading basins in the Dan region in Israel. Chloride contentsof the investigated groundwater and lsochloride lines (1992-1993), representing the spread of the treated sewage effluents in the aquifer, are included.
to the natural boron influx into the oceans, is discharged into natural water systems. Such a large anthropogenic load ought to be reflected in the boron budgets of wastewater and natural aquatic systems. Indeed, there is an enrichment of boron in both sewage effluent (up to 4.1 mg/L) and contaminated river water (1.2 mg/L) in England (15). The ratio of boron to anionic detergent (Manoxol OT) in domestic sewage has been found to be similar to that of washing powders, thus indicating that the main source of boron in domestic wastewater is sodium perborate bleach present in washing powders (15). This paper investigates the boron isotope composition of sewage effluent from the Dan Region Sewage Reclamation Project. It is asserted that the signature of anthropogenic boron should be reflected in contaminated groundwater from the Coastal Plain aquifer of Israel.
Experimental Methods Sample Collection. Treated and untreated sewage effluents were collected from the Dan Region Sewage Reclamation Project, located south of Tel Aviv (Figure 1). From 1977 to 1988 the project involved collection, treatment, recharge into the Coastal Plain aquifer, and reuse of municipal wastewater from the Dan metropolitan area (Tel Aviv-Jaffa and neighboring municipalities). The wastewater underwent biological treatment in facultative oxidation ponds with recirculation, and chemicaltreatment
by the high-lime-magnesium process, followed by detention of the high-pH effluent in polishing ponds. As of 1989, the chemical treatment has been discontinued and the process consists of only the biological treatment. The effluent is recharged to the aquifer by means of spreading basins. The wastewater, mixed with regional groundwater, is collected by recovery wells and supplied to nonpotable uses (mainly irrigation) in the south of Israel. Since the beginning of the operation in 1977, a volume of -240 X lo6 m3 of treated sewage effluent has been recharged to the aquifer (18-22). Groundwater was collected from observation and recovery wells located at various distances from the recharge basins (Figure 1). Analytical Procedure. Boron isotopic composition in sewage effluent and groundwater samples was analyzed by negative thermal ionization mass spectrometry (NTI) (23-25). The high sensitivity of the NTI technique, producing BO2- ions (11B02 and 1°B02 at amu 43 and 42, respectively), enables isotopic measurement of samples in the nanogram range, Boron was separated from natural samples by a boron-selectiveresin, Amberlite IRA-743(26). Isotopic analyses of NIST SRM-951standard and seawater solutions before and after application of the resin verified that no isotopic fractionation occurred during boron separation. Boron was eluted with 1 N HC1, mixed with a solution of MgClz and Ba(OH)Z,loaded onto Re single filaments, and measured by a reverse polarity Finnigan MAT-261 mass spectrometer. The boron blank in a 10Environ. Sd.Technol., Vol. 28. No. 11, 1994
1969
Table 2. Chemical and Isotopic Data of Treated and Untreated Sewage Effluents as well as Contaminated, Uncontaminated, and Saline Groundwater from t h e Coastal Plain Aquifer of Israel source
name
raw sewage treated sewage raw sewage treated sewage raw sewage treated sewage
R-1 RS-5 R-1 RS-5 R-1 RS-5
research well research well research well research well research well puping well puping well research well research well research well research well research well puping well puping well puping well research well research well research well research well research well research well research well research well research well pumping well pumping well pumping well pumping well pumping well pumping well pumping well pumping well
T-66 "-61 T-20 T-54 T-38 Dan 6 Dan 17 T-66 T-61 T-20 T-54 T-38 Dan 6 Dan 17 Dan 5 T-2512 T-6211 T-6212 T-26 T-29 T-6511 T-6311 T-6711 T-47 Palmachim 6 Nahi 5 Dan 5 Dan 8 Dan 3 Dan 4 Dan 6 Dan 15A
pumping well pumping well pumping well pumping well pumping well pumping well pumping well pumping well research well research well research well
Palmachim A Palmachim D Nahi 6 Dan 16 Dan 9 Dan 14 Mc. Holot Rishon 5 Machon Biology Yahum H Robin 1 Bat Yam 2
research well research well research well research well research well research well research well research well research well research well research well research well research well research well research well
Ziqim 3A p.2 Ashqelon 603-5 Ashqelon 6/C I1 Ashqelon 6/C I Ashqelon 8/A-2 Rishpon 38/B Afridar 4/A Giva'at Olga 5 l / A p.2 Giva'at Olga 51/B p.1 Giva'at Olga 51/B p.3 Y aqum D Bat Yam 11 Bat Yam 3 Hilton North Hilton 3
pumping well pumping well pumping well pumping well
Kefar Varburg A Be'er Toviyya 5 Be'er Toviyya 3 Be'er Toviwa 6 I _
1970 Envlron. Sci. Technol., Vol. 28, No. 11, 1994
well ID
lab no.
date
Sewage Effluents 72 23/3/93 73 23/3/93 153 7/6/93 161 7/6/93 199 1/9/93 200 1/9/93 Contaminated Groundwater 15112706 74 23/3/93 15212705 76 23/3/93 15112701 75 23/3/93 15212703 78 23/3/93 15112703 79 23/3/93 15112605 77 23/3/93 15012805 80 23/3/93 15112706 159 7/6/93 15212705 160 7/6/93 15112908 156 7/6/93 15212703 162 7/6/93 15112703 157 7/6/93 15112605 158 7/6/93 15012805 154 7/6/93 15212607 7/6/93 155 195 14/6/93 15112704 191 14/6/93 15112705 196 14/6/93 198 14/6/93 15112702 192 1516/ 93 194 15112804 15/6/93 15212801 197 15/6/93 190 15212707 15/6/93 15112801 15/6/93 193 43 14912501 16/8/92 14712107 2/7/91 29 2/7/91 58 15212607 59 15012602 2/7/91 2/7/91 60 15212605 2/7/91 61 15212606 2/7/91 62 15112605 15012705 2/7/91 64 Uncontaminated Groundwater 14912201 44 16/8/92 14812601 45 16/8/92 14712106 30 16/8/92 15012806 67 16/8/92 15012606 68 16/8/92 15012704 69 16/8/92 15212902 70 16/8/92 14713004 53 21/7/92 18313502 36 23/7/92 14512102 54 21/7/92 15712704 56 22/8/92 Saline Groundwater 131 28/6/92 11410402 132 28/6/92 12010712 148 12/4/90 12010810 149 12/4/90 12010810 133 24/6/92 12211002 138 27/11/90 17913304 139 12/5/90 12110801 141 14/7/91 20418802 142 14/7/91 20413901 145 14/7/91 20413904 18513501 37 23/7/92 48 15812603 15812601 57 22/8/92 1 20/9/91 16612803 3 20/9/91 16612805 Regional Study 120 12/7/92 12512401 32 13/7/92 12612402 31 13/7/92 12612403 202 1/7/93 12612301
P B (760)
C1 (mg/L)
B (mg/L)
B/CP (M)
11.2 11.0 7.6 10.3 12.9 5.3
361 332 317 308 330 330
0.49 0.46 0.62 1.06 0.60 0.63
4.453-03 4.523-03 6.373-03 1.133-02 6.003-03 6.233-03
21.9 10.4 20.1 7.8 48.0 19.5 30.3 20.8 23.3
300 364 330 303 226 229 149 272 355 346 303 225 211 140 245 202 301 322 185 373 181 312 274 315 316 202 208 177 154 195 193
3.723-03 3.183-03 4.093-03 6.163-03 1.903-03 3.943-03 1.433-03 3.673-03 5.543-03 7.173-03 5.313-03 2.163-03 3.513-03 3.123-03 3.763-03 1.093-03 3.653-03 3.183-03 5.123-03 4.703-03 5.253-04 3.273-03 3.693-03 4.723-03 7.463-03 5.883-03 4.943-03 4.173-03 4.033-03 4.713-03 5.103-03 3.373-03
15.3 17.7 24.4
112
0.34 0.35 0.41 0.57 0.13 0.28 0.07 0.30 0.60 0.76 0.49 0.15 0.23 0.13 0.28 0.07 0.34 0.31 0.29 0.54 0.03 0.31 0.31 0.45 0.72 0.36 0.31 0.23 0.19 0.28 0.30 0.12
30.5 29.3 29.8 30.7 30.8 27.7 30.1 29.6 29.3 28.0 21.5
34 70 27 85 93 46 33 67 107 99 50
0.13 0.10 0.07 0.06 0.10 0.08 0.08 0.07 0.10 0.06 0.07
1.253-02 4.873-03 8.623-03 2.123-03 3.673-03 5.493-03 8.153-03 3.483-03 3.193-03 1.993-03 4.263-03
45.7 58.5 38.4 41.8 54.2 59.7 45.1 40.0 43.9 40.0 33.2 59.0 41.6 36.9 40.3
6113 15850 17103 18257 2264 16424 2252 20100
0.79 0.82 1.08
4.243-04 1.693-04 2.073-04 1.973-04 1.293-03 2.593-04 9.713-04 8.233-04
45.6 46.2 47.6 49.9
457 404 715 711
7.2 52.3 15.0 36.4 12.7 46.8 19.4 8.0 19.9 6.8 54.1 7.1 12.0 18.5 14.5 16.6 17.8 19.0 21.1
32960 503 819 535 19812 20387
1.10
0.89 1.30 0.67 5.04 4.36 0.12 0.08 4.99 4.50
7.633-04 4.933-04 5.153-04 8.263-04 7.243-04
0.26 0.18 0.26
1.883-03 1.483-03 1.173-03
0.12
Table 2 (Continued) source pumping well pumping well pumping well pumping well pumping well a
name
well ID
Be’er Toviyya 7 Kefar Varburg D Holot Rishon 4 Nahi 5 Palmahim 6
12612302 12512302 15313001 14712107 14912501
lab no.
date
Regional Study 203 1/7/93 204 1/7/93 63 15/7/92 29 15/7/92 43 15/7/92
P B (%o)
C1 (mg/y
B (mg/L)
40.3 41.4 17.3 16.6 14.0
544 257 200 202 316
0.23 0.36 0.72
B/CP (M)
3.693-03 5.883-03 7.463-03
Values to be read as, for example, 4.45 X lo9 for 4.453-03.
mL elution was 350 ng. Since only 0.2 mL of the elution was loaded on the filament, the actual blank was -7 ng. The amount of boron loaded on the filament ranged from 50 to 500 ng of boron. The mode of filament loading and mass spectrometry procedures were strictly repeated in each sample in order to minimize the variability of mass spectrometer induced isotopic discrimination. A standard deviation of up to 2%0was determined by NIST SRM-951 replicates (25). The mean of the absolute l1B/loB ratios of 16 NIST SRM-951 replicates, analyzed along with the samples, was 3.9935 f 0.008. I t was found that addition of Ba(OH)Zenhanced ionization and production of negative ions at lower temperature, whereas addition of MgCl2 improved the reproducibility of mass spectrometic measurements (25). Concentrations of total dissolved boron were determined by spectrophotometric technique using the reagent azomethine H (26). The detection limit and reproducibility of the photometric method were 0.05 mg/L and 1-2 % ,respectively. Boron determinations in several samples were verified by isotope dilution mass spectrometry (24, 25). Chloride concentrations were determined by Ag titration with reproducibility of 2-4 % . Results and Discussion
The main sources of sodium perborate are natural sodium borate minerals (Table 1) from the United States (California) and Turkey (27). When sodium borate minerals are treated with hydrogen peroxide, sodium perborate is formed (15). It has been shown that marine borates have high 611B values (25 f 4%) relative to nonmarine borates from salt lakes associated with volcanics (-7 f 10%; ref 2). Oi and others (14)have shown that the l1B/loB ratios of sodium borates (borax, tincal; Table 1) are higher than those of sodium/calcium (ulexite) and calcium borates (colemanite, iyoite) of the same geologic origin. This is explained by the crystal chemistry of the minerals; minerals with higher B03/B04ratios have higher l1B/loBratios (14). The 611B range of nonmarine sodium borate minerals (Figure 2) from California and Turkey is 611B = -0.9 to +10.2%0 (2, 14). The 611B value of a single sample of sodium perborate (US Borax Co.), which is added to detergent powders by the detergent manufactures, is 3 f 1%. This is consistent with the 611B range of the sodium borate minerals. The 611Bvalues of the sewageeffluents (5.3-12.9%0)also overlap those of the sodium borate minerals (Figure 2). It is thus suggested that the main source of anthropogenic boron in sewage is discharged sodium perborate and natural nonmarine sodium borate minerals, mainly used in detergents. The boron contents and isotopic compositions of raw and treated sewage are similar (Table 2), indicating that the biological treatment has a negligible effect on boron balance and isotopic fractionation and does not affect the
anthropogenic signature. Therefore, boron isotope variations can be applied for tracing contamination of groundwater by both raw and treated sewage effluents. The high chloride content of the wastewater (- 350 mg/ L) relative to regional uncontaminated groundwater (-50 mg/L) is used to monitor the spread of the sewage effluents in the aquifer (18-22). A gradual decrease in chloride content with distance from the recharge basins (Figure 1) reflects mixing of recharged sewage effluents with regional groundwater. The chloride content is therefore used to determine the fraction of sewage component that mixed with regional uncontaminated groundwater. Sewage effluents from the Dan Region revealed relatively high boron content (0.5-1.2 mg/L; Table 2) associated with low P B values (5.3-12.9%0) relative to those of uncontaminated regional groundwater outside the contaminanting plume of the Dan region ([Bl = 0.05 mg/L; P B = 30%0;Figure 2). The 611B values and the high B/C1 ratios [(5-11) X suggest that sewage effluent is enriched in boron with a low 6l1B signature, relative to those of natural contamination sources, such as seawater (611B = 39%0;B/C1 = 0.8 X The distinctive boron isotope composition and the relatively high boron and chloride contents of the sewage effluents are reflected in the composition of contaminated groundwater associated with recharge of treated sewage effluents in the Dan region (Figures 2 and 3). The boron concentrations (0.03-0.75 mg/L) and the 611B values of the contaminated groundwater show, in most of the cases, a gradual increase and decrease, respectively, with increasing chloride contents (Figure 3). However, the boron contents are lower (Figure 3a) and the 611B values are higher than those of the expected theoreticalmixing curves (i.e., curve A in Figure 3b) between sewage effluent ([Cl] = 350 mg/L; [Bl = 0.6 mg/L; 611B = 10%0)and uncontaminated groundwater ([Cll = 50 mg/L; [B] = 0.05 mg/ L; 611B = 30%0). This implies both mixing of sewage effluents with regional uncontaminated groundwater and a mechanism of boron removal. The elemental boron depletion and IlB enrichment of the samples relative to the theoretical mixing curve suggest removal of boron via adsorption onto clay minerals in the aquifer (1, 3, 4, 12, 13).
The adsorption of boron onto clay is related to the boron species. Boron is present in aqueous solutions as B(OH)4ion, undissociated boric acid B(OH)s, and borates (Na,Ca,Mg)B(OH)4+. The distribution of these species is controlled mainly by the pH, as well as salinity and cation concentrations (28, 29). It has been shown that during interaction of fluids with sediments boron is taken up by clay minerals. The uptake is proportional to the concentration of boron in the solution, pH, salinity, clay content and mineralogy, clay particle size, organic carbon, cation exchange capacity, and nature of exchangeable cation. Envlron. Scl. Technol., Vol. 28, No. 11, 1994 1971
Non-matine Na-borate minerals (Oi et al., 1989)
-10
0
10
30
20
40
-
B mated sewage
50
W
50
64
contaminated seawater
Sewage effluents
scdivm perbarate
untreated
-10
0
10
30
20
treated
40
Contaminated groundwater
I
n
IW
2W
SW
4W
Chloride (mg/l)
n
IW
2W
SM
Chlonde (mg/l)
-10
d
5
lb
n
2d
30
40
50
u
60
4
Flgure 3. Chloride versus (a) boron content and (b) 6"B values of treated and untreated sewage effluentsas well as Contaminated and uncontaminated groundwater fromtheDan region. C U NA~represents hypothetical mixing behavior between sewage effluentand uncontaminated groundwater, whereas c u ~ e B s and C are the expected 6"B values of the mixing products after being equilibrated with clay minerals using m values of 0.981 and 0.969 (eq 2). respectively.
The isotopic fractionation of boron is controlled by the exchange reaction of its species, given by 'OB(OH),
Flgure 2. Histogram of 6"B values of sodium borate minerals, sodium perborate, and treated and untreated sewage effluentsas well as of contaminated and uncontaminated groundwater (from the Dan region) and saline groundwater from the Coastal Plain aquifer of Israel. N.
number of analyses. Uptake of boron by clay minerals may occur in two steps; the first is rapid and reversible, whereas the second is slow incorporation into the tetrahedral sites of the mica structure. It appears that boron adsorption by clay minerals obeys the Langmuir equation in which dissolved boron is in equilibrium with the adsorbed boron and an affinity coefficient (Kd) can be calculated for different clay minerals at any given pH. Since the affinity of the clay edges for the B(0H)d- ion is much stronger than for B(OH)3, adsorption increases with increasing pH values, up to pH of maximum adsorption (30-33). 1912 Envlron. Sci. Technol.. Vol. 28, No. 11, 1994
+ "B(oH);
= "B(oH),
+ l n ~ ( O ~ )(1) ,
Since the B(OH)3species is enriched in "B relative to the B(OH)a- species due to larger isotopic reduced partition functionratios (ll),preferentialremoval ofthe 'oB(OH),ion onto the clay edges results in isotopic fractionation in which dissolved boron (predominantly composed of B(OH), species) is enriched in I'B (12,13). It is most likely that the relative boron depletion and llB enrichment observed in the contaminated groundwater (Figure 3) reflect interactions of contaminated boronenriched groundwater with clay minerals in the aquifer. Assuming that (1) the interaction of the contaminated groundwater with clay minerals is completely reversible, (2) the content of adsorbed boron on clay minerals before adsorption is negligible, and (3) the adsorbed boron is in equilibrium with the dissolved boron (3,4,12,13,30-33), the P B value of residualgroundwater (PBm),after being equilibrated with clay minerals, can be expressed [following eq 1 in Vengosh et al. (3)lby 611B, = [(611B,,
+ lOOO)/(a- aX + X)]- 1000
(2)
where @lB.., is the 6l'B of the mixing product between
sewage and groundwater, a is the boron-isotope fractionation factor between dissolved and adsorbed boron, and X is the fraction of boron which remains in the solution [Le., it can be expressed by X = 1/(1 &), where Kd is the distribution coefficient of boron adsorption]. We used a values of 0.981 (11)and 0.969 (12)and a Kd value of 4.67 (12),which were obtained from column and seawater adsorption experiments, respectively. Solving eq 1 by using these values, we calculated the expected 611B values of the mixing products between sewage and regional groundwater after being equilibrated with clay minerals (curves B and C in Figure 3b). The P B results of all contaminated groundwater samples are higher than those of the mixing curve (A in Figure 3b), indicating isotopic fractionation associated with boron adsorption. However, most of the contaminated groundwater yielded 611B values lower than those of the equilibrated P B values expected by a values of refs 11 and 12. This may indicate that the adsorption process has not been completed and has not reached equilibrium and/or the effective water/sediment ratio is much higher than zero. It should be noted that the relatively high salinity of the sewage effluent and contaminated groundwater may enhance boron adsorption (34). In contrast, the narrow range of P B values in the chloride-depleted uncontaminated groundwater ( 30%0)suggests that boron is derived from leaching of calcium carbonate or desorption of clay minerals, mixed with meteoric water of a high P B value. A temporary leakage of seawater into the sewage network of Tel Aviv occurred at the end of August 1978. As a result, the salinity [up to 580 mg of Cl/L (35)l and composition of recharged treated sewage and consequently contaminated groundwater were influenced by this infiltration of seawater (22). High W B values (>39%0)are expected from infiltration of seawater into the aquifer (e.g., Figure 2). Therefore, some of the high 611B values ( P B of 46.8-54%0) associated with relatively low boron contents (as low as 0.03 mg/L) and B/C1 ratios of the contaminated groundwater may reflect mixing with relics of entrapped seawater. The nonlinear mixing curves which are expected upon contamination of native groundwater by anthropogenic sources enriched in boron, such as sewage effluent (Figure 3) or fly ash leachate (8), enable identification and quantification of low levels of contamination (8).Boron adsorption associated with isotopic fractionation may, however, cause a shift in the P B values of the contaminated groundwater from the theoretical mixing behavior of two components. This study shows that such a shift is limited (A8 = 10-20%0)and that the isotopic signature of anthropogenic boron in the contaminated groundwater is distinguishable from that of natural groundwater in the study area. The isotopic signature of anthropogenic boron is also different from those of natural saline sources in the Coastal Plain aquifer of Israel. The P B values of marine-derived saline groundwater along its western margin are between 35% and ~ O % O(Figure 2). These high P B values are associated with lowB/Clratios, indicating removal of boron by adsorption, e.g., the Dead Sea where 611B = 57%0(3). Thus, salinization of groundwater by intrusion of seawater or marine-derived brines into the aquifer is reflected by high 611B values (39-60%0)and low B/C1 ratios (0.2 x 10-3 whereas contamination by anthropogenic to 0.8 X
saline groundwater
I
+
N
1.o
0.5
0.0
1.5
Boron (mg/l)
i uncontamnated groundwater
contamnated groundwater raw sewage
m treated sewage
A
saline groundwater (interface zone)
0
Regional study Beer Toviyya
4 Regional study
Flgure 4. 611B values (%o) versus boron content (mg/L) of sewage effluent, Contaminatedand uncontaminatedgroundwater from the Dan region, saline groundwater from the Interface zone, and several contaminated wells (reglonal study) from the Coastal Plain aquifer of Israel. Curves A-C represent hypothetical mixlng behavior between uncontaminated groundwater and sewage effluent, seawater, and seawater after being equilibrated with clay minerals, respectively. The vector rosette describes schematically the effect of adsorptlon process. Note the differences of 611Bvalues in several contaminatedwells. The high 611Bvalues of groundwater from the saline plume of Be‘er Toviyya reflect salinization by natural, marinederived saline groundwater.
sources, such as recharge, irrigation, or leakage of sewage effluents, is associated with low P B values and high B/C1 ratios (Figure 4). In order to apply this new method, the variations of boron isotope ratios in several contaminated pumping wells from the Coastal Plain aquifer were examined (Table 2). The isotopic results and the B/Cl ratios clearly indicate that some wells (Holot Rishon 4, Nahi 5, Palmahim 6) were contaminated by anthropogenic boron having a low P B signature and relatively high B/C1 ratios, whereas others (Be’er Toviyya 3, 5, 6, and 7 and Kefar Warburg A and D) reflect natural sources. For example, the high salinity and low 611B value (14%0) of well Palmahim 6 is directly related to sewage contamination, in agreement with its shallow depth (38 m) and location near the contaminated Soreq River in an area irrigated by treated sewage. On the other hand, the association of high salinity with high 611B values from wells in the Be’er Toviyya area (Figure 4) reflect input of natural, marine-derived saline water, as previously suggested by Vengosh and Ben-Zvi (36). Conclusions The combination of high boron content coupled with a readily distinguished isotopic signature makes boron a good tracer for identification of sources of anthropogenic contaminants, particularly of sewage effluent. Moreover, elemental boron and boron isotope composition can be used for monitoring the accumulation of organic pollutants in groundwater. Since a large fraction of the surfactant Environ. Sci. Technol., Vol. 28. No. 11, 1994
1973
compounds in detergents is subject to biodegradation in aerobic environments, resulting in a wide spectrum of biodegradation intermediates (37-39)) boron can also be used to trace surfactants in aquatic systems. The distinctive isotopic composition of anthropogenic boron relative to those of regional uncontaminated groundwater and natural saline sources makes boron isotope composition a potential environmental tool for tracing the origin of dissolved constituents and, hence, sources of contamination in groundwater. The large isotopic differences of boron sources (natural versus anthropogenic) and the adsorption of boron onto clay minerals enables tracing of the origin, migration, evolution, and reactivity of fluids in and with aquifer rocks. Acknowledgments
This study, a joint German-Israeli research project, was supported by the Bundesministerium fur Forschung und Technologie, Germany (BMFT) and Ministry of Science and Technology, Israel (MOST). We thank W. Giger and two anonymous reviewers and appreciate their rapid and thorough review. We thank Y. Kolodny (Hebrew University) for reviewing an early version of the paper, Rami Keren (Volcani Center) for helpful discussions, Eva Klein (Volcani Center) for carrying out some of the boron measurements, Adam Kanarek and Avi Aharony (Dan Region Sewage Reclamation Project) for field work assistance, and M. Collin (Hydrological Service) for improving the language of the manuscript. Literature Cited (1) Schwarcz, H. P.; Agyei, E. K.; McMullen, C. C. Earth Planet. Sci. Lett. 1969, 6, 1-5. (2) Swihart, G. H.; Moore, P. B.; Callis, E. L. Geochim. Cosmochim. Acta 1986,50, 1297-1301. (3) Vengosh, A.; Starinsky, A.; Kolodny, Y.; Chivas, A. R. Geochim. Cosmochim. Acta 1991,55, 1689-1695. (4) Vengosh, A.; Chivas, A. R.; McCulloch, M. T.; Starinsky, A.; Kolodny, Y. Geochim.Cosmochim.Acta 1991,55,25912606. (5) Vengosh, A.; Starinsky, A.; Kolodny, Y.; Chivas, A. R.; Raab, M. Geology 1992,20, 799-802. (6) Land, L. S.; Macpherson, G. L. Am. Assoc. Petrol. Geol. Bull. 1992, 6 , 1344-1362. (7) Vengosh, A. Ph.D. Thesis, The Australian National University, Canberra, Australia, 1990. (8) Davidson, G. R.; Bassett, R. L. Enuiron. Sci. Technol. 1993, 27, 172-176. (9) Bassett, R. L. Appl. Geochem. 1990,5, 541-554. (10) Buszka P. M.; Bassett, R. L.; Davidson, G. R. EOC, Proc. Am. Geophys. Union 1991, H42D-6. (11) Kakihana, H.; Kotaka, M.; Satoh, S. Bull. Chem. SOC. Jpn. 1977,50, 158-163.
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Received for review March I , 1994. Revised manuscript received June 8, 1994. Accepted July 8, 1994.' Q
Abstract published in Advance ACS Abstracts,August 15,1994.
